This invention is generally directed to toner and developer compositions, and more specifically the present invention is directed to conductive carrier compositions. In one embodiment of the present invention, the carrier compositions are comprised of a mixture of certain carrier cores with optional polymeric coatings thereover. Specifically, the carrier particles of the present invention in one embodiment are of a conductivity of from about 10.sup.4 to about 10.sup.10 (ohm-cm).sup.-1, in one specific embodiment of the present invention, there are provided developer compositions containing a mixture of carrier particles with coatings thereover, which coatings have dispersed therein conductive particles such as carbon black, and wherein the carrier particles are of a conductivity of from about 10.sup.4 to about 10.sup.9 (ohm-cm).sup.-1 as determined, for example, in a cell wherein a current of from about 1 to about 1,000 volts is utilized. Generally, the carrier particles of the present invention are comprised of a mixture of high, such as steel grit cores, and moderate, such as a nickel zinc ferrite carrier, conductivity carrier particles. Developer compositions can be formulated by mixing the aforementioned carrier particles with toner compositions comprised of resin particles, pigment particles, and optional additive particles inclusive of charge enhancing components, colloidal silicas, and metal salts of fatty acids. Some advantages associated with the carrier particles of the present invention include, for example, the modification of magnetic brush properties present in electrophotographic imaging systems including properties of stiffness, conductivity, ability to retain conductivity with varying amounts of toner, and the like. Moreover, with the conductive carrier particles of the present invention the toner triboelectric charging properties remain relatively constant for extended imaging cycles up to, for example, 100,000. The toner and developer compositions of the invention are useful in electrophotographic imaging and printing processes, including color processes. Further, with the toner and developer compositions of the present invention, there is enabled in the aforesaid processes substantial uniformity of the toner triboelectric charge for extended time periods. Moreover, the toner and developer compositions of the present invention enable photoconductive imaging members or ionographic receptors present in an imaging or printing apparatus to function without adverse effects for extended time periods, for example, exceeding 100,000 imaging or printing cycles.
Various developer compositions are known, reference for example U.S. Pat. No. 3,926,824, which discloses a developer with two toners and a single carrier; two carriers and a single toner; or a single toner and a single carrier, see the Abstract of the Disclosure, and column 2 begininng at line 52. As illustrated in column 2, beginning at around line 60, of the '824 patent, a single toner and two different carriers with at least a surface of the two carriers being formed of materials being selected with respect to their triboelectric properties so that one of the carriers is above and the other below the toner in the triboelectric series whereby one carrier imports a negative charge to the toner, and the other carrier imports a positive charge to the toner isrecited. Examples of specific carriers are illustrated, for example, in column 8 of the aforementioned patent. A similar teaching is presented in U.S. Pat. No. 4,038,076. Further, in U.S. Pat. No. 4,608,603 there is described the use of carrier particles consisting of a steel core, or a ferrite core with polymeric coatings thereover. In U.S. Pat. No. 4,272,184, there are illustrated conductive carriers with a resistivity of from about 10.sup.7 to about 10.sup.10 ohm-cm wherein the core may be seleted from iron, steel, ferrite, magnetite, nickel, and mixtures thereof, reference column 8, lines 42 to 55. Additionally, of background interest is U.K. Patent Publication No. 2,088,076, which discloses a developer comprised of two toners having different conductivities. Also, developer and toner compositions with certain waxes therein are known. For example, there are disclosed in U.K. Patent Publication No. 1,442,835 toner compositions containing resin particles, and polyalkylene compounds, such as polyethylene and polypropylene of a molecular weight of from about 1,500 to 6,000, reference page 3, lines 97 to 119, which compositions prevent toner offsetting in electrostatic imaging processes. Furthermore, the '835 publication discloses the addition of paraffin waxes together with, or without a metal salt of a fatty acid, reference page 2, lines 55 to 58. In addition, many patents disclose the use of metal salts of fatty acids for incorporation into toner compositions, such as U.S. Pat. No. 3,655,374, the disclosure of which is totally incorporated herein by reference. Also, it is known that the aforementioned toner compositions with metal salts of fatty acids can be selected for electrostatic imaging methods wherein blade cleaning of the photoreceptor is accomplished, reference U.S. Pat. No. 3,635,704, the disclosure of which is totally incorporated herein by reference. Additionally, there are illustrated in U.S. Pat. No. 3,983,045 three component developer compositions comprising toner particles, a friction reducing material, and a finely divided nonsmearable abrasive material, reference column 4, beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted, fatty acids preferably of from 8 to 35 carbon atoms, or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43.
Illustrated in copending application U.S. Ser. No. 004,939/87, the disclosure of which is totally incorporated herein by reference, are toner and developer compositions with linear polymeric alcohols comprised of a fully saturated hydrocarbon backbone with at least about 80 percent of the polymeric chains terminated at one chain end with a hydroxyl group, which alcohol is represented by the following formula: EQU CH.sub.3 (CH.sub.2).sub.n CH.sub.2 OH
wherein n is a number of from about 30 to about 300, and preferably of from about 30 to about 100, which alcohols are available from Petrolite Corporation. Coated and uncoated carrier particles are disclosed in the aforesaid copending application.
Furthermore, references of background interest are U.S. Pat. Nos. 3,165,420; 3,236,776; 4,145,300; 4,271,249; 4,556,624; 4,557,991 and 4,604,338.
Moreover, toner and developer compositions containing charge enhancing additives, especially additives which impart a positive charge to the toner resin, are well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. There are also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Further, there are illustrated in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer and toner compositions with charge enhancing additives, organic sulfate and sulfonate compositions; and in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions containing resin particles and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds, inclusive of cetyl pyridinium chloride. The '390 and '672 patents also disclose carrier components for developers, including coated carrier cores. Other prior art disclosing positively charged toner compositions with charge enhancing additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 and 4,394,430.
Although the above described toner and developer compositions are useful for their intended purposes, there is a need for improved compositions. More specifically, there is a need for carrier compositions with certain conductivities. There is also a need for developer compositions comprised of the aforementioned carrier particles and toner particles. In addition, there is a need for toner and developer compositions that maintain their triboelectrical characteristics for extended time periods exceeding, for example, 150,000 developed images, and wherein the carrier particles are comprised of a mixture of core components with coatings thereover enabling the carriers to possess a conductivity of from about 10.sup.4 to about 10.sup.10 (ohm-cm).sup.-1. Furthermore, there is a need for colored developers that possess many of the aforementioned characteristics. There are also a need for carrier and developer compositions including color developer compositions wherein modification of the magnetic brush properties present in an electrophotographic imaging apparatus can be accomplished independent of the charging properties of the toner compositions including the brush properties such as stiffness, conductivity, and the ability to retain conductivity when toned. There is also a need for carriers which are coated with similar or substantially identical polymers and contain conductive particles therein, and wherein the coating weights are adjusted to enable similar charging properties with the toner composition selected especially the colored toner compositions. Moreover, there is a need for toner and developer compositions, particularly developers containing carrier blends comprised of a mixture of two different carrier cores, that is a first carrier core and a second carrier core, thereby enabling enhanced developer in, for example, electrophotographic imaging and printing apparatuses, it is believed, because of the combined characteristics of the different cores.